a. Field of the Invention
The instant invention is directed toward a template system and methods for use on a tissue, e.g., for ablation procedures. In particular, the template system of the present invention comprises a track which may be anchored to the tissue, and guides a transducer for ablation and other procedures.
b. Background Art
Normal heart rhythm is between 60 and 100 beats per minute. Tachycardia is a fast heart rate (usually over 100 beats per minute) caused by disease or injury. Tachycardias may begin in the upper chambers of the heart (the atria) or the lower chambers of the heart (the ventricles). Some tachycardias are harmless, but other tachycardias are life threatening. With this disorder, the heart does not fill with enough blood between beats to meet the needs of the body. Tachycardias can quickly deteriorate to fibrillation.
Atrial fibrillation (AF) is the most common abnormal heart rhythm. It is a very fast, uncontrolled heart rhythm that occurs when the upper chambers of the heart (the atria) try to beat so fast (between 350 and 600 times per minute) that they only quiver. Ventricular fibrillation (VF) occurs when the lower chambers of the heart (the ventricles) produce impulses that make the heart beat too quickly. Fibrillation is a life-threatening arrhythmia demanding immediate treatment.
Before a tachycardia deteriorates to fibrillation, various procedures may be used to treat the heart tissue and reduce or altogether eliminate the occurrence of fibrillations. It is well known that treatment benefits may be gained by forming lesions in tissue if the depth and location of the lesions being formed can be controlled. These lesions block the errant electrical signals that result in the tachycardia. In particular, it can be desirable to elevate tissue temperature until thermally necrosed lesions are formed which change, i.e. reduce or eliminate the electrical conductivity of the tissue. For example, when “good” or “sufficiently deep” lesions are formed at specific locations in cardiac tissue, undesirable fibrillations may be lessened or eliminated. The definition of “good” or “sufficiently deep” when describing lesion formation depends at least to some extent on the procedure and may also depend on other considerations, such as tissue characteristics and desired results. In general it is currently thought that transmural lesions are desired (i.e., lesions extending from the endocardium to the epicardium). However some recently reported work demonstrates this may not always be true.
Several difficulties may be encountered with existing ablation or lesion-making techniques. For example, during minimally invasive ablation procedures on a patient's heart, a physician makes a small incision in the patient's abdomen for insertion of an ablation wand. The wand may have a radio-frequency (RF) electrode on the tip for delivering ablative energy to the heart tissue. The physician must maneuver the tip of the wand adjacent the heart tissue to be ablated (the “target area”). The physician may determine placement of the wand based on his/her experience maneuvering the wand during the ablation procedure. Such experience only comes with time, and may be quickly lost if the physician does not perform ablation procedures on a regular basis. In the case of MIS surgery the target tissues are not in the surgeon's direct line of sight.
Even an experienced physician may find it difficult to maneuver the wand. For example, an extended wand inserted through a small incision in the patient's abdomen severely limits the physician's ability to manipulate the tip of the wand in the desired direction near or on the heart. In addition, the axis of the wand may not be aligned with the desired lesion axis, thereby requiring the physician to reposition the wand so that the physician can pull the wand in the direction needed to form a linear or curvilinear lesion. Even after properly positioning the wand, it is often difficult to drag the wand at a constant velocity and at the appropriate angle to achieve a uniformly deep and wide lesion.
When these procedures are performed on the heart, the beating heart further complicates matters by making it difficult to assess placement of the wand adjacent the tissue during the time needed to form the desired lesion. That is to say that one would not want the wand moving uncontrollably, as by random lateral slippage or sliding, during the procedure. If the wand is not properly controlled, a quality lesion is unlikely to be formed and the procedure may be unsuccessful, needing to be repeated to achieve the desired result. In addition, there may be undesirable damage to the surrounding tissue. So lesions are typically made by a stationary or otherwise fixed ablator (relative to the tissue to be ablated) or are made with a controllably scanned or moved ablator. In either case, the energy deposition is predictable for all tissue ablated.
Thus, there remains a need for controlled placement and movement of ablation means during ablation procedures.